System for remotely transferring voltages as a measure of antenna beam scanning in radar apparatus



Sept- 21, 1954 T. .1.V JOHNSON, JR., ETAL 2,689,952

\ SYSTEM F 0R REMOTELY TRANSFERRING VOLTAGES AS A MEASURE 0F ANTENNA BEAM SCANNING IN RADAR APPARATUS Filed Dec. 29, 1950 5 Sheets-Sheet l OECZERS/NG VL MGE ivi Sept. 21, 1954 T. J JOHNSON, JR., ErAL SYSTEM FoR REM 2,689,952 oTELY TRANSFERRING voLTAGEs As A MEASURE 0F ANTENNA BEAM scANNING IN RADAR APPARATUS 5 Sheets-Sheet 2 Filed Dec. 29. 1950 Sum. c

Awww uw- No.

INVENTORS Sept 21, 1954 T. J. JOHNSON,

SYSTEM FOR REMOTELY TRANSFERRI JR. l' AL NG VOLTAGES AS A MEASURE OF ANTENNA BEAM SCANNING IN RADAR APPARATUS 3 Sheets-Sheet 3 Filed Dec. 29 1950 @www I I l l l l l l i I I l l l I l I L #TQQQQQSQQM mmbb /MHS d. JOHNSON, Je. LV/A/ G. VHA/HSH/NE INVENTOR$ @fram/EVS Patented Sept. 2l, Y1954 UNITED STAT PATENT FFME SYSTEM FOR REMGTELY TRANSFERRING VOLTAGES AS A MEASURE F ANTENNA BEAM SCANNING IN RADAR APPARATUS fornia Application December 29, 1950, Serial No. 203,304

16 Claims.

The present invention relates to improved means and technique whereby information as to the angular position of a radar antenna beam in the process of scanning is transmitted from the site of the antenna to a remote location, which may be as much as two miles from the antenna location, for effecting operation of an indicating system located at such remote location.

The present invention contemplates an improvement in a ground controlled approach (G. C. A.) radar system in which antennaJ for producing the scanning beam may, for example, be located adjacent an aircraft landing strip with the associated indicator located at a remote position as, for example, in the control tower which may be located as much as two miles from the antenna itself.

In such systems, the movement of the cathode ray sweeps in the indicator is synchronized with movement of the scanning motion of the antenna beam and, in the usual precision part of a ground controlled approach (G. C. A.) system, a voltage is developed at the antenna which varies in magnitude with the angular position of the antenna beam, and this voltage is conveyed over suitable lines to the indicating system. This developed or generated voltage usually varies substantially linearly with movement of the antenna beam when and as such beam moves from one extreme angular position to the other extreme angular position, and vice versa, with the antenna beam scanning periodically only a fractional part of a circle. The rate of antenna beam scan is usually one scan per second, and accordingly the voltage thus varies cyclically at a corresponding rate of one cycle per second.

it is extremely important, for purposes of accuracy, in systems of this type, that the Voltage at the indicator be truly representative of the voltage developed in the movement of the antenna. Diiliculties have heretofore been encountered in transmitting this voltage from the antenna to the indicator, especially in those installations where the distance between the antenna and indicator is relatively long and the conductors connecting such stations are subjected to interference resulting, for example, from electromagnetic or electrostatic coupling between the transmission line cable which serves to convey such voltage and nearby power line cables.

It is therefore an object of 'the present invention to provide improved means and technique whereby the voltage appearing at an indicator is truly representative of the voltage generated or developed upon scanning movement oi the associated antenna beam, whereby accurate representations may be obtained on the indicator.

A specific object of the present invention is to provide an improved G. C. A. system in which the so-called angle voltage developed upon movement of the scanning beam of the precision antenna located adjacent the aircraft landing strip, which scans in opposite directions cyclically at a low frequency of, for example, one cycle per second, is transmitted with fidelity to an indicator for effecting operation of the same in, for example, a remotely located control tower.

Another specic object of the present invention is to provide improved means and technique of this character which incorporates a pulse-time modulated system of coding in which the time interval between 'two successive pulses is a measure of the instantaneous angle of the antenna beam while scanning cyclically through a fractional part of a circle.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its organization and manner of operation, togetherI with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure 1 shows in schematic form an improved ground controlled approach (G. C. A.) system embodying features of the present invention;

Figure 1A shows the variation of voltage developed in accordance with movement of the beams of the two antennas in the precision section of a G. C. A. radar system;

Figure 2 is a circuit diagram showing the components of the amplitude comparator which is designated in block form in Figure l;

Figure 3 shows in schematic form the components designated in block form in Figure l as peak detector and storage, rectifier for increasing voltage, rectiiier for decreasing voltage, switch tube and storage;

Figures 4, 5, 6, 7 and 8 are graphic illustrations helpful in understanding the operation of the antenna angle integrating assembly shown in block form in Figure 1 and the operation of the circuit shown in Figure 3.

Figure 1 shows in schematic form the precision section of a G. C. A. radar system which includes an elevation antenna l and an azimuth antenna ll, each of which is arranged to produce an antenna beam that alternately scans the aircraft landing approach zone respectively in elevation and in azimuth. The particular means whereby these antenna beams are alternately oscillated through a fractional part of a circle is not indicated in Figure 1, but their oscillatory movements are represented respectively by the curved arrows H3A and l IA. These antenna beams may be produced by the variable Wave guide type of antenna structures described in the copending patent application of r`Karl A. Allebach, 'Serial No. 49,910, led September 18, 1948, now Patent No. 2,596,113, and assigned to the same assignee as the present invention.

Voltages are developed having magnitudes which are proportional to the particularangular positions of the antenna beams-fin -their scanning movements; and, for this purpose, the angle coupling voltage generators IEIB and IIB are mechanically coupled respectively to the elevation and azimuth antennas for development of voltages which are alternately applied through the single pole double throw switch I3 tothe-.amplitude comparator Ill. Such voltages applied to the amplitude comparator I4 are represented in full lines in Figure 1A, and it is noted that they vary substantially linear from low values corresponding to one'extreme position of the antenna beam to maximum values corresponding to the other extreme position of vthe antenna beam.

The angle voltage remoting apparatus described in greater detail hereinafter is used on a time-sharing basis-since, as seen in Figure 1A, the voltage variations I6, I1, I8 and I9 are each transmitted in that order for a period of approximately one-fourth of a second, It is noted that the voltage developed in the angle-coupling voltage generators IIlB and IIB are represented in Figure 1A and vary cyclically and synchronously at, for example, three cycles per second, corresponding to three scans or" the antenna beam per second; and, as indicated previously with reference to Figure 1A, selected portions only, on a time-sharing basis, of the azimuth and elevation voltage variations are applied to the amplitude comparator in the antenna beam angle remoting assembly 26.

It is these voltages, i. e., the so-called angle coupling voltages, which vary with time as represented in Figure 1A, that are required to be transmitted with delity to the indicator section I5 (Figure 1) located, for example, a distance of two miles from the antenna. The present invention concerns itself particularly with the means and technique wherebytsuch angle coupling voltages, represented in full lines in Figure 1A, are transmitted from the site of the antenna to the remotely located indicator section I5.

The angle coupling voltage variations I6, I8 and I'I, I9, correspond respectively to movements of the azimuth and'elevation antenna beams, with the variations I6 and ITI representing movements of the azimuth and elevation antenna beams, respectively, in, forexample, a clockwise direction; and the variations I 3 and I 9 represent the movements of these same antennabeams, respectively, in the opposite direction, i. e., the counterclockwise direction.

These voltage variations I6, I'I, I8 and I9 are applied in that order tothe-amplitude comparator I4, through relay switch I3, the operation vof which is timed to achieve this result by the application of energizing currents to the Az-El (azimuth-elevation) relay winding 9 in accordance with movement of the antenna beams. In general, each of these voltage variations I6, I1, IS and I9 applied to the comparator I4 are used in generating a pair of pulses, i. e., a so-called reference trigger 30 and a data trigger 3l, the data trigger 3l occurring a variable time interval afterthe referencetrigger with such time interval serving as a measure of the instantaneous value ofthe antenna beam angle voltage, either eleva- 'dataytriggers tion or azimuth beam angle voltage, as the case may be.

This pair .ofpulses, i. e.,'the so-calledreference trigger and data trigger, are each developed in the antenna beam angle remoting assembly 26 using the radar system trigger which is generated in the synchronizer unit 2B, and such reference and data .triggers are transferred over a pair of coaxial transmission lines 2|, 22, respectively, to the remotely located antenna beam angle integrating assembly 23.

The antenna beam angle integrating assembly 23 functions to reconstruct the voltage variations I6, I'I, I8 and I9 from the received reference and The elevation and azimuth beam angle coupling voltages thus derived in the assembly 23 and appearing at the output terminals of the assembly 23 are applied through the single pole vdouble throw switch 21 to both the sweep limiter and sweep amplifier stages 28, 29, respectively, of the character described in the copending application of Tasker et al., Serial No. 776,702, led September 29, 1947, for Single Scope Two Coordinate Radar Systems, now Patent No. 2,649,581, and a-ssigned to the same assignee as the present invention. In general, these azimuth and elevation beam angle coupling yvoltages thus derived in the assembly 23 are used to modulate the cathode ray sweeps in such a manner that the angular position of the cathode ray sweeps correspond to the instantaneous angular position of the corresponding azimuth or elevation antenna, as the case may be, with however resulting unidirectional expansion in the displays appearing on the cathode ray tube in the indicator section.

Briefly, the apparatus for transmitting andreceiving pulses as shown in Figure 1 includes a central timing and synchronizing unit or synchronizer 29, a modulator and transmitting oscillator or transmitter stage 33, an antenna system which includes: the elevation antenna I6, the azimuth antenna II, the transmission line 39 for feeding energy from the transmitter stage 33 to the antenna Ill, the transmission line 35 for transferring energy from the transmitter stage 33 to the antenna II, and a pair of plates 36,31 on opposite ends of a crank arm 33 which is rotated at a substantially constant speed by a motor 39, with such plates 36, 3l being arranged to alternately prevent the flow of energy through such transmission lines 3d, 35, whereby the antennas IU and II are alternately fed by energy from the transmitter 33. In other words, energy is supplied to the antennas Iii, I I from the transmitter stage 33 on a time-sharing basis. A transmitreceive switch (TR switch) [i9 interconnects the receiver 4I with the antenna system. The video output from the receiver is applied to the video amplifier stage 92 in the indicator section I5, and after amplification is applied to one of the elements of the cathode ray tube 93 for eiecting intensication of the cathode ray beam as a result of the received echoes.

Also, as indicated hereinbefore, and described in greater detail hereinafter, a synchronous tie exists between movement of the antenna beams radiated from the antennas IIJ and II and the cathode ray sweeps generated in the cathode ray tube 43.

In general, the synchronizer 2i) generates a pulse which is applied to the modulator and transmitter stage 33, and such pulse is also applied to the electrical time measuring circuit in the indicator I5, speciiica-lly to the sweep amplifier 29, to start the electrical time measuring circuit, i. e., to initiate radial outward movement of the cathode ray beam sweeps.

Also, in accordance with important features of the present invention, the pulses from synchronizer 25 are applied to the 250 microsecond gate generator lid in the remoting assembly for production of the aforementioned reference trigger Also, mechanically coupled to the elevation and azimuth antennas l0, il are the blanking switches 45 and 4E, respectively, the output of each of which is transferred to the sweep amplier 29 for purposes of blanking, i. e., rendering invisible the cathode ray trace at predetermined times. Further, the blankingswitch 46, when energized, serves to close an energizing circuit for the two azimuth-elevation (Az-El) relay windings il and lil, for time-sharing purposes. Each of the relay windings I1 and 4l are serially connected respectively with voltage sources I'I'A and MA. These windings Il, il are energized in Figure l and are thus effective to hold the switch contacts I3 and 2l, respectively, in a downward position against the action of the corresponding coil tension springs i5A and 27A; when the windings H and il are deenergized Athese springs I3A, 21A effect upward movement of the attached sweep elements i3 and 2l to condition the apparatus for conveying information with respect to the elevation antenna; and when the windings Il and di' are energized the apparatus is conditioned for supplying information with respect to the azimuth antenna. Actually, the movements of the crank arm 38, voltage generators IUB, IiB and blanking switches 45, G6 are all synchronized in a manner described in greater detail in the above mentioned copending patent application of Tasker et al., Serial No. 776,702.

To facilitate description of the operation of the remoting assembly 2t and integrating assembly 2d, it is assumed that the switches I3, 2l remain in the positions shown in Figure l, i. e., the indicator system l5 is in a condition to display information obtained when the antenna beam produced by the azimuth antenna i I scans through space and during the occurrence of voltage variation I5 (Figure 1A).

Antenna beam angle rc1/noting assembly Briefly, with reference to Figure 1, trigger pulses from the synchronizer 25 are applied, at a rate of, for example, 2,000 per second to the input circuit oi a 250 micrcsecond gate generator, with the result that negative gating voltages #58,

having a time duration of 250 microseconds and with a repetition rate of 2,000 per second, are delivered to the differentiating stage [i5 whereby the leading and trailing edges of the gating voltages are differentiated to produce respectively the positive peak 50 and negative peak 5I at the output of the differentiating stage 139. Such pulses 5t, 5i are applied to the blocking oscillator stage 52 which is receptive substantially only -to the positive peak 5i), and such oscillator stage 52 functions to produce the sharp reference triggers 3Q at its output terminals. Such reference triggers 30, occurring with a repetition rate of 2,000 per second are applied to the inner conductor of the coaxial transmission line 2i; and likewise such triggers 3s are applied to the 200 microsecond gate generator 5t to produce negative gating voltages 5t, each having a time duration of 200 microseconds. Such negative gating voltages 54 initiate operation of the sawtooth generator 55, and the output of the generator 55, in the form of sawtooth waves 56 is applied to the amplitude compara-tor Ill, wherein the changing amplitude of the sawtooth wave 55 is compared with the voltage being generated by the angle coupling voltage generator I IB and shown, at this particular time, as the voltage variation I-S in Figure 1A.

The amplitude comparator le functions, when the amplitude of the sawtooth wave 55 is substantially equal, at the instant considered, to the magnitude of the voltage I5 (Figure 1A), to produce the positive pulse 5l. Such positive pulse 5'I is differentiated in the differentiating network 58 to produce the negative voltage wave peak 59 and positive voltage wave peak 60; and, the voltage pulse thus differentiated is applied to the blocking oscillator stage Eil which is receptive substantially only to the positive peak 6G. ln response to such positive peak 60 the blocking oscillator BI generates the sharp data trigger 3l which is applied to the inner conductor of the coaxial cable 22 for transmission to the remotely located antenna beam angle integrating assembly. It is important to observe at this -time that while the reference and data triggers 35, 3l respectively have the general shape and are applied over different transmission lines, the data trigger occurs a predetermined time interval after the occurrence of the reference trigger 35, and that such time interval between the pulses et, 3i is a measure of the voltage generated in the voltage generator I IB and represented by the variation it in Figure 1A. The reason for lthis is made clear from the description which follows with respect to Figure 2, which shows in greater detail the circuitry in the amplitude comparison stage is.

In Figure 2, the sawtooth voltage waves 55, of 200 microsecond duration (time for rise of the wave from minimum 4to maximum Value is 200 microseconds), are applied to the control grid til of the cathode follower tube 65, while the voltage developed in the voltage generator EIB (Figure l) applied to the control grid 66 of the cathode follower tube 5l. The anodes of tubes 55 and 5l are connected to the positive ungrounded terminal of voltage source 53. The cathode of tube 65 is connected to one terminal of the output load resistance l0, which has its other terminal connected to the negative ungrounded terminal of voltage source l2. Likewise, the cathode of tube 5l is connected to one terminal ol the resi-stance '53, which has its other terminal connected to the negative terminal of the voltage source 12.

A fractional part of the saw-tooth wave appearing across resistance 'it is applied to the control grid l5 of the tube 75 which, in the quiescent state, is normally non-conducting for reasons mentioned hereinafter. Specically, the control grid i5 is connected to an intermediate point on the resistance li, resistance 'lil being used to establish the proper voltage level at grid 'd5 of tube it.

It is observed, from a study of Figure 1A that the voltage variation i6, now under consideration, as well as the other voltage variations I 7, i8 and I5, all represent positive values of voltage, and such positive voltages are applied to the control grid 5S to cause the tube 5l to conduct space current. Such space current ows through the resistance li, and the resulting voltage developed across resistance i3, which is likewise connected between the cathode "Il and the negative terminal of source l2, imposes a suiiiciently high bias on the control electrode i5 to thereby render the tube 73 non-conducting (in the absence of sawtooth wave 56, i. e., in the quiescent state). It should be carefully observed that such bias voltagexonezcontrol gridl T varies in amplitude in accordance with the instantaneous magnitude of the voltage variation i9. The tube 79 is rendered conducting only when the instantaneous amplitude of the sawtooth wave 59 applied to control gridV 'I5 substantially equals the bias voltage. In this -respect it should likewise be carefully observed that a definite time is required for such sawtooth wave to reach such amplitude whereby the tube 19 is rendered conducting so that space current may flow through the output load resistance 18, which is connected between the anode of tube 16 and the positive terminal of source 69. Such current flow through resistance 'i8 results in production of the positive pulse 57 (Figures 2 and 1), which is applied to the differentiating network comprising the serially connected condenser '19 and resistance 99. It is noted that one terminal of condenser i9 is connected to the anode of tube 79; that one terminal of resistance 89 is connected to the grounded cathode 83; andA that the junction point of condenser 19 and resistance 80 is connected to the grid of tube 92, which has its anode connected to the positive terminal of source |59 through resistance 8e. The tube 82 thus serves essentially as an amplifier stage having the output thereof in the form of peaked voltage waves 59 and 69 applied through condenser 85 to the blocking oscillator stage 6| in Figure l. The blocking oscillator 9|, as mentioned previously, is receptive substantially only tothe positive peaked wave 60 and functions to produce a sharply defined data trigger 9|.

It is important to note that the data trigger 3| lags the reference trigger 30 by a time interval which is a measure of the instantaneous voltage applied to the control grid 96. This is so since a definite time interval is required for the sawtooth voltage applied to grid l5 to assume a magnitude sufcient to render the tube 70 conducting. This time lag between the reference trigger and data trigger 9| is thus Within 200 microseconds while, of course, the voltage applied to control grid 96 varies at a relatively small rate, as observed in Figure 1A. While the time involved in one complete voltage variation I6 is Vin the order of one-fourth of a second, it is noted that the sawtooth voltage waves applied to control grid 75 occur at a much higher repetition rate of 2,000 per second.

The reference and data triggers 90 and 3| thus developed in the remoting assembly 49 are transmitted to the remotely located integrating assembly 23 over separate transmission lines 2| and 22, respectively. The function of the integrating assembly, as described in detail hereinafter, is to reconstruct the original voltage variation I6, Il, I9 or i9, as the case may be, from information supplied to the same in the form of variable spaced reference and data triggers.

Antenna beam angle integrating assembly 23 As mentioned above, the purpose of this assembly is to reconstruct the voltage variations shown in full lines in Figure 1A, using the reference trigger 30 and data trigger 3| transmitted over the separate coaxial cables 2 I 22.

These triggers 30, 3| received at the assembly 23 may rst, if desired, be applied to separate amplifier stages (not shown) before being applied to the blocking oscillators 90 and 9|, respectively, for resharpening the triggers 30, 3| which may have been distorted and thus lost their sharpness in transmission. The reference trigger is applied to the blocking oscillator 90,.

after amplifcationfdesired, .and the output of the blocking oscillator is inthe form of-two sharp negative pulses or triggers 92 vand 93, occurring simultaneously, while the output of the data trigger blocking oscillator 9| is in the form of a positive trigger 94. The reference trigger 92 initiates operation of the gating voltage generator 95, and the following data trigger 94 serves to terminate the gating Voltage being produced in response to the trigger 92. Thus, the gating generator 95 serves to generate negative gating voltages 99, the duration of .which is variable infaccordance with the time interval between the reference trigger` 92 and data trigger 94.

The variable width gate 96 thus produced initiates operation of the sawtooth generator 91, which generates a voltage increasing'at a constant rate. The length of the sawtooth voltages generated by generator 97 is determined by the width of the pulse 9G', so that the maximum value of the sawtooth wave is a measure of the width of the pulse 99, and thus a measure of the time interval between the triggers 92 and 99. The output of the sawtooth generator 97 is peak detected in the peak detector and storage stage 98. Associated with the peak detector instage 98 is a storage device, in this instance a capacitor, which serves to maintain the positive peak values of detected voltage during successive operations of the sawtooth generator 9T. The unidirectional voltage thus appearing on the capacitor in stage 99 is applied, through a D. C. level setting stage 99, to a gated clamping circuit |0|, such clamping circuit |0| being gated by gating voltage developed in the gate generator 95. The capacitor in the peak detector stage 98 is periodically discharged by the reference trigger 93 applied to such stage. The output of the cathode follower stage |09 is in the form of the voltage variations shown in Figure 1A, and such voltage variations are applied through the time switch 27 to the sweep limiter and sweep amplifier stages 28, 29 for producing that type of indication set forth in the aforementioned copending application of Tasker et al., Serial No. 776,702.

To improve the operation of this circuit 'described generally above, a feedback path |02, including an adjustable phase shifting circuit |03, is connected between the cathode follower output stage and sawtooth generator 91. In general, this feedback circuit serves to avoid lag in operation of this integrating assembly.

This integrating assembly 29, while described in general with reference to Figure l above, is described in greater detail with reference toy Figure 3. The reference trigger 39, either amplified or not, as desired, is applied to the control electrode |04 of the tube |05, which has its cathode grounded and its anode connected to the positive terminal of voltage source 06 through the winding |01 of the blocking oscillator transformer |08, which includes also the windings |09 and ||0. Tube ||2 has its cathode grounded and its control grid connected through winding |09 and resistance ||4 to the negative ungrounded terminal of voltage source H5, such resistance H4 and source ||5 being shunted by the capacitor The anode of tube |2-is connected to the anode of tube |95. The other winding ||0 has one of its'terminals grounded and the other one of its terminals. connected to supply a negative reference trigger 92 to the cathode i I8 of the tube |20. Also, the connected anodes of tubes |05 and I|2 are connected through the condenser |2| and diode |22 to the ungrounded 9 terminal of the condenser |24 for periodically discharging such condenser, using the negative trigger 93.

Specifically, the condenser I2| is connected to the cathode |39 of diode |22 and the anode |3| is connected to the ungrounded terminal of condenser |24. Further, such cathode |34 is connected to ground through resistance |33. The anode |35 of tube |36 is grounded and the associated cathode |37 is connected to the ungrounded terminal of condenser |24.

The gate generator 95 functions to produce variable width gating voltages which are applied to the control grid |39 of the tube |39 of the sawtooth generator stage 97. The voltage applied to such grid |38 comprises. a variable width gate represented at |45.

In general, the operation of the gate generator 35 is such that the negative trigger 92 initiates formation of the gating voltage, while the data trigger |4| supplied from the blocking oscillator |42 terminates such gating voltage, the length of the gating voltage thus being a measure of the spacing between the reference trigger pulse 93 and the data trigger |4|. For this purpose the anode |45 of tube |29 is connected through resistance |49 to the positive terminal of voltage source |39, and such anode |45 is connected to the cathode |49 and the ungrounded terminal of condenser |59. The anode II associated with the cathode |49 is connected to the output of the blocking oscillator stage |42 to receive the pulse I4|. The operation of the gate generator 95 is briely as follows: In the quiescent state the anode |45 has a voltage determined by the voltage on condenser |53, i. e., the Voltage drop across resistance |43 resulting from the space current flowing from the positive terminal of source |95 through resistance |46 and through the grid cathode of tube |39 through resistor |54 to the negative source |56. Upon the application of the negative trigger 92 to the cathode H9, the condenser |59 is charged negatively. After disappearance of the reference trigger 93 the potential of anode |45 is maintained sub'- stantially at that depressed potential, inasmuch as the condenser |50 discharges at a relatively slow rate, the condenser |59 having, for example, a capacity of 680 micromicrofarads and the resistance |45 being in the order of 2.2 megohmsI Subsequently, the positive trigger |4| applied through the diode, which comprises the elements I5! and |49, discharges the condenser |59 to terminate the gating voltage thus formed.

The variable Width gating waves., represented at 95 and |49 in Figure 3, are applied both'to the control grid |33 of the sawtooth generator stage 97 as Well as to the clamping stage |0|, which incorporates a pair of triodes, such clamping stage ||l| being gated, in a manner described hereinafter, by such Variable width gating voltages 95. The cathode |52 of tube |39 is connected to ground through the cathode resistance |53; and also through resistance |54 to the negative ungrounded terminal of the bias voltage source |56. The anode |58 of tube |39 is supplied with a regulated voltage, and for that purpose is connected through a series circuit comprising: the resistance |58, the diode |59, resistance I5|l to an adjustable tap on the potentiometer resistance |62, which has one of its terminals grounded and the other one of its terminals connected to the ungrounded terminal of the voltage regulator tube |65, such ungrounded terminal of tube |65 being connected through resistance |37 to the positive terminal voltage source |05.

rlhe circuit elements associated with tube |39 described above are intended to stabilize the operation of the sawtooth generator stage 57 to such an extent that it is stable in operation and functions satisfactorily with replacement tubes for the tube |39, even though the characteristics of such replacement tubes are somewhat different. To achieve this general purpose, the anode |58 of tube |39 is connected to the cathode |79 of diode |7I which has its anode |72 grounded. By thus providing tube and returning the cathode |52 to a negative return, i. e., the negative terminal of source |55, the operation of this stage 97 is stabilized. It is noted that the voltage at the anode |58 of tube |39 is determined. by the potential which is necessary to cause space current to flow in diode |7I. This circuit is thus stabilized for variations in the characteristics of tube |39. Tube serves to stabilize the sawtooth generator for variations in the positive supply voltage |95.

In the quiescent state, i. e., in the absence of a gating Voltage 95, the grid |39 of tube |39 is clamped at zero volts or slightly positive with respect to the cathode |52. This results from space currentl flowing from the positive ungrounded end of supply |95 through the large resistor |45 to the grid |33 of tube |39. As a result of the grid-cathode voltage thus obtained the anode space current is caused to be at the saturation or maximum value. This will cause the voltage on anode |68 to be depressed to its lowest value, slightly negative, as limited by the fraction of a volt which will cause diode I7I to conduct space current. The current which flows through resistor |53 during this quiescent period is established by the potential at the cathode |70 of diode |7| (a fraction of a volt negative) and by the potential set at the cathode |84 of diode |59 by variable resistor |52. When the negative gate 9E is applied to grid |38, the anode space current of tube |39 is caused to cease. This action causes the voltage on the capacitor combination |6| and |32 to start rising toward the positive voltage at the cathode |84 of diode |59 at a rate determined by the capacitance of capacitor combination |8| and |82 and the resistance of resistor |58. The rising voltage on capacitor combination |8| and |32 is applied to the grid |77 of the cathode follower which is made up of tube |73 and resistor |80 The output from the cathode of tube |73 is connected to the opposite end of resistor |58 from the `ca pacitor combination |8| and |82. Thus the rising voltage at the capacitor combination I8I and |82 is applied to both ends of resistor |58, i. e., one end by the direct conductive connection and the other end by the cathode follower tube |73 and capacitor |83. Since the same rising voltage displaced only by a direct current drop appears at both ends of resistor |58, a steady current flows through this resistor. This steady current which can flow only into the capacitor combination |3| and |82 causes this voltage to rise completely linearly with time. Diode |59 acts in such a manner as to isolate the charging circuit from the positive supply during the sawtooth rise in voltage. All of the charge which is transferred to capacitor combination ISI and |82 is supplied by capacitor |33.

The cathode follower tube |73 has its control grid |77 connected to the anode |68 and its anode |78 connected to the positive terminal of agesegea ll source |99, while the cathode |19 is connected through the load resistance |99 to the negative terminal of source |56. The cathode |19 is connected through resistance |99 to the junction point of condensers |8| and |82, the condenser |82 having one of its terminals grounded and condenser |9| having one of its terminals connected both to the anode |99 and control grid |11. Also, the cathode |79 is connected through ggidenser |99 to the cathode |99 of the diode Thus the sawtooth Waves |25 have a variable length corresponding to the variable length of the gating voltage |99, which in turn is determined by the time interval between the reference trigger 93 and data trigger E9 i.

The sawtooth voltage waves |75 appearing on the cathode |29 are applied to the peak detector and storage stage 99, and specifically to the control grid |85 and anode |89 of tube |87. The cathode |99 of tube |91 is connected to the ungrounded terminal of the condenser |24, as well as to the control grid |99 of the cathode follower tube |92,

It is noted that there is no discharge path, as such, for the charge accumulated in condenser |29, but such condenser |29 is discharged periodically and in timed relationship with appearance of the reference trigger pulse 93. As a matter of fact, this reference trigger 93 is applied through the diode |22 to effect discharge of the condenser |29. Thus, the voltage across the condenser |29 is clamped to zero upon the occurrence of each reference trigger pulse. However, subsequently, this condenser |25 is charged at a substantially linear rate in accordance with the rate of rise of the sawtooth voltage Wave IIS, and the ultimate voltage on the condenser |24 after disappearance of the sawtooth wave |15 assumes a value which is a measure of the maximum value the particular sawtooth attained in its rise. This maximum value of volta-ge in condenser |2li is maintained until the appearance of the succeeding reference trigger 93 which serves to discharge such -condenser |29. Thus, the voltage across condenser 24 varies as a function of time either in accordance with the full line graph |93 in Figure 5 or the full line graph |99 in Figure 7, depending respectively upon whether or not the triggers 93 and I4! represent, at the particular instant concerned, increasing voltages such as voltage variations I9 and in Figure lA, or decreasing voltage variations as represented at i8 and i9 in Figure lA.

In Figures and 7 the locus of the peaks of the full line curves are represented by the dotted lines |95 and |95, respectively, and it is such continuous voltage variations as represented by such curves |95, |99 which are desired to be applied to the sweep amplier and sweep limiter 29 and 28 (Figure l) in the indicator section of the radar system. In other Words, it is desired that the steps in the voltage waves |93 and |99 be eliminated as much as possible, and for that purpose generally the gated clamping circuit |9| (Figure 1) is utilized to efectively disconnect the condenser |29 from the sweep amplier 29 and sweep limiter 29 (Figure 1) during the time such steps are being produced. The circuit described hereinafter is intended to accomplish this general result, and to derive the voltage variations |91 and |98 (Figures 6 and 8), respectively, from the more stepped voltage variations |99 and |99.

4Comparing Figures 4, 5, 6, '7 and 8, they each represent voltage variations as a function of time on the same time base.

Figure 4 represents, inA

full lines; the voltage 'outputof the'sawtooth generator asa result of a successive Vseries of pulses 93, IM, and the dotted line in Figurefi indicates the locus of peaks of theseY saWtooth waves and shows that these sawtoothy waves increase inI amplitude, i, e., increase in amplitude as the time interval between pulses 93 and |9| increases. Figure 5 shows in full lines the resulting voltage output of the peak detector stage 99, and the full linevaration |92' in Figure 'representsitlie voltage variation appearingy inv the output terminal |99 in' Figure 3. Figure i'shows voltagevvariations corresponding to voltage variations lshown in Figure 5, but such variations in Figure7 are the result of recurrent sawt'o'oth voltage'iwaves of decreasing amplitudeyi. e., voltage variations in Figure 7 correspond to the condition-wherein the time interval between successive sets ofi reference and data triggers 93 and |4| decreases. Figure 8` shows a voltage variation appearing' at the output terminal |99 in response tothe voltage variation shown in Figure?.

The manner in which the voltage variations in Figures 6 and 8 are obtained respectively from the corresponding voltage variations of Figures 5 and '7 is now described in' detail with reference to Figure 3. The voltage variation of Figure. 5 is thus applied to the control grid |99'in` Figure 3. Associated anode 299r of the cathode follower tube |92 is connected to the positive terminal of source |99, while the cathode'292`is connected to the negative terminal of source y'|59 through the potentiometer resistance 294 and resistance 299, the adjustable tap on resistance '299being connected to the cathode 295 and anode 299' of the tubes v291 and 298, respectively. It isnoted that for purposes of establishing the correct voltage level the resistance 299 is connected in shunt with the voltage regulator tube 2|9vv and bypassed by a condenser' 2H. llhus, -an adjustable voltage may be applied from the adjustable tap on the resistance 295| to the'cathodef295fand anode 299. Further, the voltages appearing yon the cathode tube 292 are applied through the coupling condenser 2|l5` to the interconnect-ed cathode 295 and anode 299.

In general, the tube 297 serves asa clamper for decreasing voltages appearing on the-cathode 292; and the other tube-299 serves in similar capacity as a clamper for increasing voltages appearing on the cathode 292. In otherwords, the tube 291.' is effective to transfer voltages to the cathode follower output stagev 2|5, while'the peak detector output .voltage decreases; while the tubev 299iseffective to'transmit voltages to the cathode follower outputv stage2|9 during' the time the voltage output of the peak detector'increases. This statement 'is' qualied, h"owever,'to the extent that tube 291 is ineffective: in transferring such decreasing voltages, at the timethis tube 291 is being rendered non-conducting bythe application of the gating voltage 99 thereto through the coupling condenserZ H.

It is noted that the setting of the variable tap on the potentiometer resistance 299i adjusts the direct current level at which the; tubes 29"! and 298 are eiective toconduct.

For these general purposes the cathode 218` of tube 299 and the anode 2-|9 of tube-291 are'interconnected and connected? to the control*v grids of the parallel connected cathode follower tubes 22 222, as well as to the ungrounded terminalof condenser 229. The control g'ridi2251ofl tube-,291 is connected to one terminal fofrcondenser' 2|1,

`as well as-'tothe associated. cathode 295 lthrough resistance 227. Thus, the gating voltages applied through coupling condenser 2| l are applied to the control grid 225 of tube 201. The negative gating voltages transmitted through condenser 2H to the grid 225 appear, at substantially the same time, as the sawtooth waves applied to the storage condenser |24, i e., during the rising portions of the full line voltage variations |93 and I Sil, respectively, in Figures 5 and 7. During such time interval the interconnected control grids 234, 235 are effectively disconnected from the cathode 202, and thus such grids 23d, 235 are rendered substantially insensitive to the rising voltages appearing on the cathode 2532. This results in a more continuous voltage applied to the control grids 23d, 235. The anodes of cathode follower tubes 22|, 222 are connected to the positive terminal of source |639, and their interconnected cathodes are connected to the angle voltage output terminal |99 as well a-s to the negative terminal of voltage source |5 through the output resistance 220.

In order to prevent sluggishness in operation, i. e., to overcome lag in the circuit elements, a feedback path 2M is provided, such feedback path 24| extending from the output terminal |99 to the ungrounded terminal of the potentiometer resistance 242. The adjustable tap on the resistance 222 is connected through condenser` 243 to the anode of tube |59, whereby voltage variations appearing on the output terminal |99 are transferred back to the sawtooth voltage generating stage 9i with an adjustable phase shift determined by the setting of the tap on resistance 2112. By this feedback connection 24|, the anode H68 of the sawtooth generating tube |39 is rendered more positive for increasing voltages appearing at terminal |99; and conversely the potential on anode |63 is rendered more negative when decreasing voltages appear at terminal |99. The adjustment of the tap on resistance |52 likewise affects the potential of anode |68, but such adjustment is static in nature, whereas the feedback connection 22|, while producing generally the same functions, i. e., controlling the potential of the anode |68, is dynamic in nature with the voltage on the anode |68 changing in accordance with the voltage conditions at terminal |29.

The voltage thus appearing on the output terminal |99 is applied, as shown in Figure 1, through the AZ-El relay switch 21 to both the sweep limiter 23 and sweep amplifier 29 for producing their effect on the cathode ray tube indicator. This voltage thus applied varies, for example, from 2 volts to 52 volts or from 52 volts to 2 volts, as the case may be, in accordance with the variations shown in Figure 1A. These voltage variations, as shown in Figure 1A, are relatively slow, whereas the reference and data triggers occur at a relatively high repetition rate of 2,000 per second. These voltages appearing in Figure 1A are thus reconverted when and as the time interval between the reference and data triggers varies from, for example, 50 microseconds to 150 microseconds, i. e., when the time interval between the reference trigger and data trigger is 50 microseconds the voltage appearing at the output terminal |99 is 2 volts; and when the time interval between the reference and data triggers is 150 microseconds the voltage appearing at the output terminal |99 is 52 volts. In other words, the time differential of 100 microseconds, i. e., 150 minus 50, corresponds to a voltage Variation of 50 volts, i. e., 52 minus 2.

The range of Voltage variation in general is adjusted by adjusting the position of the tap on the resistance |62, whereas in general the level at which such voltage variation occurs is adjusted by adjusting the position of the variable tap on the resistance 204.

Preferably, the reference trigger 92 follows the system trigger generated in the synchronizer 20 (Figure 1) by 250 seconds, such time differential being established by rst applying the trigger from the synchronizer 20 to the 250 microsecond gate generator il@ in the remoting assembly 26. This condition is desirable since the listening time for radar echoes lasts for approximately only microseconds after the system trigger. Thus, the antenna angle information is sent over the transmission lines 2|, 22 after arrival of all of the video information to avoid interference and simplify the decoding apparatus at the remote location.

While it is preferred to use two coaxial cables 2|, 22 for this purpose, the same information as developed herein may be transmitted over a single coaxial cable if desired.

While the particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. In a system of the character described, antenna means for producing an electromagnetic beam comprising pulses of radiated electromagnetic energy at a relatively high rate, means periodically delivering said electromagnetic energy to said antenna means, echo receiving means coupled to said antenna means for receiving echoes in response to reflections of said electromagnetic energy, means periodically moving said antenna beam to produce a scanning movement thereof at a relatively low rate, means deriving a continuously varying voltage in accordance with said scanning movement, with the instantaneous magnitude of said voltage being a measure of the particular angular position of said beam, means operated synchronously with said delivering means and deriving a pair of pulses spaced in time in accordance with the instantaneous magnitude of said voltage, means at a remote location recreating said voltage in accordance with the time interval between said pair of pulses, and said pulse deriving means incorporating delay means whereby said pair of pulses occur after reception of all echoes resulting from one transmitted energy pulse.

2. In a system oi the character described, antenna means for producing an antenna beam comprising pulses of radiated electromagnetic energy at a relatively high rate, a transmitter coupled to said antenna means to recurrently deliver said electromagnetic energy thereto, trigger generating means for periodically initiating operation of said transmitter, means producing scanning movement of said beam, means deriving a continuously varying voltage the instantaneous amplitude of which is a measure of the particular instantaneous angular position of said antenna beam in its scanning movement, said scanning movement being at a relatively low cyclical rate, reference and data trigger generating means coupled to said trigger generating means l5 anditolsaidfvoltagerderivingllmeansfforfprdducing a@ reference andldata'trigger' with`=a timeinterval tlfi'erebetvveenv which. is a .measure Ofi `the .instan- 'taneousfvalue ofv said voltage',` voltage recreating meansI coupled to said: referenceV and:v data trigger generating m'eansi'or re'converting said voltage iin accordance with.thespacingfbetweent said reference andy data triggers, and .indicating meanscoupled to said Voltage'recreating means.

l3. .The arrangement' set forthv in 'claim 2f in which .echo-receiving. means is coupled to'- said antennaxmeansztof receive' echoes resulting-.from reflectionsof 'said electromagnetic beam, and rsaid reference vand:data/trigger generating-means includes-V delay means' whereby a pair of said'reference` and data triggers are formed` after reception of substantially all.echoesiresultingfrom one.y .transmitted energy pulse;

4::Inza system of the character described,` an antenna beamsanglefremoting assembly comprising: a' n'rst` gating voltage generator, triggerfgenerati'ngl meansA coupledl to and periodically initiating operation of saidirst gatingz'voltage-generator to produce a'rstgatingvoltage of'relativelylongiduration, adifferentiating network cou-v pledftosaid rst gating voltage generator to produce-peaked voltages of opposite polarity corresponding .respectively to the leading andr trailing edges of-.saidrst gating voltage, means coupled to said differentiating network for deriving a sharpened reference trigger which corresponds to the trailing edge of .said rst gating voltage, a rst transmission line coupledtothe last mentioned means for transferring said reference trigger to a remote location,.a second gating voltage generatorv coupled to said last mentioned means. for producing a second gating voltage of relatively long duration with the beginning of said second gating voltage. corresponding. to the trailingedge of said .iirst gating voltage, a sawtooth generator' coupled to said second gating voltage generator to. periodically form sawtooth voltage waves in accordance with the time duration of said second. gating voltage, an amplitude comparison stage coupled to said sawtooth generator, antenna beam scanningv means producing anantenna beamscanning through space, means derivinga voltagewhich Varies continuously ata relatively small cyclical rate -in comparison/withthe. repetition rate ofsaid rst gating Voltage with the.

instantaneous magnitude of said voltage representing the instantaneous angular position of rsaidfantenna beam, said amplitude. comparison stage. incorporating meansY whereby. the instantaneous magnitudes of said sawtooth and last.

mentionedv voltages are compared, and whereby. a third gating voltage is produced when the .magnitudes of said voltages differ a predetermined constant amount, a differentiating network coupled to said amplitude comparison stage for deriving peaked voltages Acorresponding respectively to the lead-ingfand trailing edges ofsaid third gating voltage, data trigger generating. means coupled to the last mentioned diiierentiatingnetwork for deriving a data trigger voltage inaccordance with one of the last mentioned peaked voltages, and a second transmission line coupled to-said data trigger generating means.

5. In a system of the characterdescribed, an oscillating antenna beam scanning periodically through a fractional part of a circle,.means.deriving in timed sequence substantially linearly Varying voltages whichcontinuously. increase or continuously decrease, depending. respectively upon the direction of oscillating movement. of .the

lr6 antennafbeam, means developing a pair of pulses spaced:.a time. interval whichisA a measure of the instantaneous magnitude` of said continuously varying voltages, and means recreating said'continuously varyingvoltagesin response to the time interval between said pulses.

6. In a system' of the character described, an oscillatingfant'enna beam moving first in one dire'ctionand then in the other reverse direction nscanning space, said antenna beam oscillating at a' relatively low frequency, means deriving a continuouslyincrea'sing voltage and a continuously decreasing voltage, respectively, when and as saidantenna beam moves in'said one direction and in s'aidotherv direction, pulseforming means developing a reference pulse and a companion data pulse with such. pulses spaced a time intervalwhichis a measur'eof theinstantaneousvalue of said increasing'voltage or decreasing voltage, as the casemay be, said pulse forming means incorporating lmeans whereby said reference pulse and its companiondata pulse are generated at' a'relatively'high repetition' rate compared to therate' of oscillating movement of said antenna beam, andfmeans recreating said continuously increasing voltage and continuously decreasing voltage in resp'onsetothev time interval between saidreference and. data pulses.

7. IInt a system ofv the character described whereinit is desired to transmit information as to.` the fangular position. of'Y an antenna'beamf to f a remotely located. point', the improvementiwhich comprisesdeveloping azvoltage the magnitude'of which variescontinuously'in accordance-with the angular position of saidantenna beam, deriving' a referenceyanda data pulse separate'dbyv a time interval which is a measure ofthe magnitude of such voltage, transmitting said' referencel and data pulses to said remotelylocated point, and

'deriving fromV said reference and data pulses a Voltage varying inmagnitude iniaccordance with the' time 4interval "betweenfsaid Yreference and: data pulses.

8. In a system of thev character described, an

'azimuth antenna forming an azimuth beam, an

elevation antenna forming an elevation beam,

`each of saidazimuth and elevation beams oscillating generally throughv the same space, means coupled to each of. said azimuth and elevation antennasfor. producing continuously increasing or continuously decreasingvoltages corresponding-respectivelyv to whether the-azimuth and. elevation'beams `are'being movedy outwardly. or inwardly in their oscillatoryA movement, means de- I r-iving` apair or spaced-pulses, the time'interval between which .is a-measure of the. instantaneous magnitude of. said .increasing or decreasingr voltage, -as-the case may be, means forming a substantially continuously increasing and a substantiallycontinuously decreasing voltage inre- -sponsetothetime interval between said pulses.

9...-In. a. system ofthe character. described,4 an antenna. beamf..angle. integrating assembly comprising afirst blocking oscillator stage having. its

`input; terminalconnected to a-first cable for receiving reference triggers, a second cable, a' second-blockingl oscillator having its input terminal connected to-said second cable. to vreceive data triggers, a gating voltage generator for generatinggating voltages of variable Widths, the operation. of. saidfgating voltage4 generator -being initiated. by -pulses delivered thereto fromsaid first blocking oscillator, the operation. of saidgating voltage generator being terminated by pulses de- `livered'thereto-from saidsecond blocking oscillator stage whereby the width of the gating voltage generated in said gating voltage generator is determined by the time interval between the triggers supplied thereto by said first and second blocking oscillators, respectively, a sawtooth generator coupled to and operated by gating voltages delivered thereto from said gating voltage generator, said sawtooth generator incorporating means whereby the duration of the sawtooth voltages generated therein is determined by the length of the gating voltages delivered thereto, a peak detector and storage stage coupled to said sawtooth generator, said peak detector and storage stage including a condenser which is periodically charged with a voltage determined by the maximum value of the sawtooth voltage applied to said detector stage, means coupling said irst blocking oscillator to said peak detector and storage stage for discharging said condenser in timed relationship with the reference triggers coupled to said blocking oscillator stage, indicating means, a gated clamping circuit coupling said condenser to said indicating means, and means coupling the gating voltage to said clamping circuit to render said circuit inoperative as a coupling circuit during the duration of said gating Voltage.

10. In a system of the character described, a gating voltage generator, said generator incorporating means for generating a gating voltage the duration of which is determined by the time interval between reference and data trigger voltages applied thereto, a sawtooth generator coupled to said gating voltage generator and incorporatingvmeans for generating sawtooth voltage waves having a substantially constant rise rate and with the duration of the sawtooth determined by the duration of the gating voltage whereby the peak value of the sawtooth voltage wave is determined by the duration of the gating voltage supplied thereto, a peak detector and storage stage coupled to said sawtooth voltage wave, said peak detector and storage stage incorporating a condenser charged periodically and in accordance with the maximum magnitude of the sawtooth voltage Wave delivered to said peak detector and storage stage, means periodically discharging said condenser in timed relationship with the appearance of reference trigger voltages, a voltage utilization device, a clamping circuit coupling said utilization device to said condenser, and means coupling said gating voltage generator to said clamping circuit to render the same inoperative during the duration of the gating voltage.

11. The arrangement set forth in claim in which a feedback circuit is connected between the output of said coupling stage and said sawtooth generator for overcoming sluggishness in operation of the system.

12. In a system of the character described in which it is desired to transmit information as to the angular position of an antenna beam scanning through space to a remote location, the improvement which resides in deriving a continuously varying voltage, the instantaneous magnitude of which is a measure of the particular angular position of the antenna beam, deriving a pair of spaced reference and data triggers with a time interval between the same varying in accordance with the particular magnitude of said voltage, transmitting said reference and data triggers to said remote location, and recreating at said remote location a voltage which varies in magnitude in accordance with the spacing between said reference and data triggers.

13. In a radar system of the character described wherein pulses of electromagnetic energy occurring at a relatively high repetition rate are supplied to antenna means to form an antenna beam, and wherein said antenna beam is caused to scan through space at a relatively low cyclical rate compared to the aforementioned repetition rate, and wherein receiving means is coupled to said antenna means to receive echoes resulting from reflections of said electromagnetic beam, and wherein information as to the particular position of said antenna beam in its scanning movement is transmitted to a remote location, the improvement which resides in deriving a continuously variable voltage, the instantaneous magnitude of which is a measure of the particular angular position of said antenna beam in its scanning movement, deriving from said voltage a pair of trigger voltages after reception of substantially all echoes and with the time interval between said trigger voltages being a measure of the instantaneous magnitude of said voltage, transmitting said pair of trigger voltages to a remote location, and recreating at said remote location a voltage which varies in magnitude in accordance with spacing between said pair of trigger voltages.

14. In a system of the character described, wherein it is desired to transmit a low frequency continuously varying Voltage indicative of the angular position of an antenna from a sending station to a remote receiving station, the improvement which resides in transforming, at said sending station, said voltage into a pair of spaced pulses of relatively high frequency, the time interval between which is representative of the instantaneous magnitude of said varying voltage, and converting said pair of spaced pulses, at the receiving station, into a voltage representative of the original voltage.

15. In a system of the character described, wherein it is desired to transmit from a sending station to a remotely located receiving station, a continuously varying voltage indicative of the angular position of an antenna, and wherein said antenna has periodically applied thereto pulses of radio frequency energy with a relatively high periodicity, the improvement which resides in converting said voltage into a pair of spaced pulses having the aforementioned periodicity, with the spacing between said pulses representative of the instantaneous magnitude of the voltage, and means for converting, at said receiving station, said pair of pulses into a continuous voltage varying with a relatively low periodicity.

16. The arrangement set forth in claim 15 in which the pair of pulses transmitted from said sending station to said receiving station is delayed and appears a substantial time interval after the supply of each of said radio frequency energy pulses to said antenna.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,412,670 Epstein Dec. 17, 1946 2,419,340 Easton Apr. 22, 1947 2,448,016 Busignies Aug. 31, 1948 2,459,482 Bond Jan. 18, 1949 2,519,935 Smith et al Aug. 22, 1950 2,539,905 Herbst Jan. 30, 1951 2,552,172 Hawes May 8, 1951 2,552,303 Anderson May 8, 1951 2,554,172 Custin May 22, 1951 2,585,855 Sherwin et al. Feb. 12, 1952 

